Various industries involve the mixing of cement and one or more additives to create a cement slurry having desired characteristics. For example, in the hydrocarbon exploration and production arena, cement is used for various cementing work in the underground wells, such as to affix the casing inside the well. Cement additives may be available in a variety of forms, such as powder and liquid. For cement slurry used in hydrocarbon wells, a variety of types of additives may be used, such as to modify the characteristics of the slurry or set cement. Examples of additives are accelerators, retarders, fluid-loss additives, dispersants, extenders, weighting agents, lost circulation additives and special additives designed for specific operating conditions.
In many applications, the cement slurry may be delivered across long distances and/or the slurry and set cement may be subject to high temperatures and pressures. For example, in some wells, Portland cement is used as the base material mixed with silica sand designed to prevent the cement from cracking at high temperatures, and one or more retarders to cause the cement slurry to stay liquid for a desired period of time. The proper proportions and type of additives used in the slurry can significantly affect cement performance. Poor cement performance can lead to substantially increased cost and loss of valuable time and revenue.
Various currently known techniques for blending cement may have one or more drawbacks or limitations. For example, existing “air bulk blending” and similar techniques often require first the loading of cement, followed by additives and then more cement into a mixing tank. High pressure air is blown inside the tank to push the cement up and down and blend the components. At completion of the blending job, the blender is emptied into containers for delivery. This process is not continuous—it requires interruption at the beginning and end of each blending job to load and unload the materials. It also requires on-site material handling personnel. Further, the blending job is limited to the volume capacity of the mixing tank. In some instances, potentially harmful dust may be spread into the ambient air in the work area. Sometimes, the cement and additives may be contaminated by moisture in the air during mixing, experience premature chemical reactions and/or adhere to the tank wall. Often, material segregation occurs in the mixing tank due to the differing specific gravities of the components because they are not continuously stirred and agitated, leading to a non-uniform slurry product. Further, low specific gravity components may float in the air, be carried away in vent lines and lost from the blended slurry.
It should be understood that the above-described features and examples are provided for illustrative purposes only and are not intended to limit the scope or subject matter of the appended claims or those of any related patent application or patent. None of the appended claims or claims of any related application or patent should be limited by the above discussion or construed to address, include or exclude each or any of the cited examples, features and/or disadvantages, merely because of the mention thereof herein.
Accordingly, there exists a need for improved systems, apparatus and methods for blending cement having one or more of the attributes or capabilities described or shown in, or as may be apparent from, the other portions of this patent.